U.S. patent application number 15/826663 was filed with the patent office on 2019-05-30 for apparatus, methods and systems for dynamic ventricular assistance.
The applicant listed for this patent is Richard Wampler. Invention is credited to Richard Wampler.
Application Number | 20190160213 15/826663 |
Document ID | / |
Family ID | 66634690 |
Filed Date | 2019-05-30 |
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United States Patent
Application |
20190160213 |
Kind Code |
A1 |
Wampler; Richard |
May 30, 2019 |
APPARATUS, METHODS AND SYSTEMS FOR DYNAMIC VENTRICULAR
ASSISTANCE
Abstract
Systems methods are disclosed for changing one or more
characteristics (e.g. flow magnitude via pump speed) of mechanical
circulatory assistance provided by an LVAD during specified points
in the cardiac cycle, preferably using closed loop control. The
system and method may be implemented for dynamically changing
ventricular unloading during the cardiac cycle by adjusting the
degree of ventricular assistance during systole and/or diastole.
The system and methods also include a means to sense the phase of
the cardiac cycle to inform the LVAD of timing within the cardiac
cycle.
Inventors: |
Wampler; Richard; (Loomis,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wampler; Richard |
Loomis |
CA |
US |
|
|
Family ID: |
66634690 |
Appl. No.: |
15/826663 |
Filed: |
November 29, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/024 20130101;
A61B 5/4836 20130101; A61M 1/122 20140204; A61M 1/1005 20140204;
A61B 5/0402 20130101; A61M 1/1086 20130101 |
International
Class: |
A61M 1/10 20060101
A61M001/10; A61M 1/12 20060101 A61M001/12; A61B 5/024 20060101
A61B005/024 |
Claims
1. An apparatus for providing mechanical circulatory assistance
provided by an implanted left ventricular assist device (LVAD)
pump, the apparatus comprising: (a) a processor; and (b) a
non-transitory memory storing instructions executable by the
processor; (c) wherein said instructions, when executed by the
processor, perform steps comprising: (i) receiving data relating to
a physiological parameter of a circulatory system in which the
implanted LVAD pump is operating; (ii) identifying diastolic and
systolic phases of the cardiac cycle of the circulatory system; and
(iii) controlling the speed of the pump to have a different speed
during the diastolic phase than during the systolic phase.
2. The apparatus of claim 1, wherein controlling the speed of the
pump comprises increasing the speed of the pump during the
diastolic phase as compared to the systolic phase.
3. The apparatus of claim 2: wherein said increased speed during
the diastolic phase results in an increased pumped diastolic
volume; and wherein said increased pumped diastolic volume
contributes to a smaller end diastolic volume and a diminished
starling response associated with a left ventricle of the
circulatory system.
4. The apparatus of claim 1, wherein controlling the speed of the
pump comprises decreasing the speed of the pump during the systolic
phase as compared to the diastolic phase.
5. The apparatus of claim 4: wherein said decreased speed of the
pump during the systolic phase results in an increased pumped
diastolic volume; and wherein said increased pumped systolic volume
contributes to a decrease in pressure in an aorta associated with
the circulatory system.
6. The apparatus of claim 1, wherein controlling the speed of the
pump comprises applying a different speed during the diastolic
phase than during the systolic phase for specified intervals that
are spaced by periods of rest.
7. The apparatus of claim 6, wherein the specified intervals
comprise periods of one or more of decreasing speed during the
diastolic phase and increasing speed in the systolic phase to
incrementally reduce assistance provided to the circulatory system
by the pump.
8. The apparatus of claim 1: wherein receiving data relating to a
physiological parameter comprises measuring a current applied to
the pump; wherein said current is correlated to an output of the
pump and the diastolic and systolic phases of the cardiac cycle;
and wherein said instructions when executed by the processor
further perform steps comprising identifying the diastolic and
systolic phases of the cardiac cycle as a function of the measured
current over time.
9. The apparatus of claim 1: wherein receiving data relating to a
physiological parameter comprises measuring a physiological
parameter with a sensor; wherein said physiological parameter is
correlated to an output of the pump and the diastolic and systolic
phases of the cardiac cycle; and wherein said instructions when
executed by the processor further perform steps comprising
identifying the diastolic and systolic phases of the cardiac cycle
as a function of the measured physiological parameter.
10. The apparatus of claim 9, wherein the physiological parameter
comprises one or more of electrocardiogram measurements,
ventricular pressure measurements or ventricular volume
measurements.
11. A method for providing mechanical circulatory assistance
provided by a left ventricular assist device (LVAD) pump, the
method comprising: installing an LVAD within a circulatory system
of a patient; receiving data relating to a physiological parameter
of the circulatory system; identifying diastolic and systolic
phases of the cardiac cycle of the circulatory system; and
controlling the speed of the pump to have a different speed during
the diastolic phase than during the systolic phase.
12. The method of claim 11, wherein controlling the speed of the
pump comprises increasing the speed of the pump during the
diastolic phase as compared to the systolic phase.
13. The method of claim 12: wherein said increased speed during the
diastolic phase results in an increased pumped diastolic volume;
and wherein said increased pumped diastolic volume contributes to a
smaller end diastolic volume and a diminished starling response
associated with a left ventricle of the circulatory system.
14. The method of claim 11, wherein controlling the speed of the
pump comprises decreasing the speed of the pump during the systolic
phase as compared to the diastolic phase.
15. The method of claim 14: wherein said decreased speed of the
pump during the systolic phase results in a decreased pumped
diastolic volume; and wherein said decreased pumped systolic volume
contributes to a decrease in pressure in an aorta associated with
the circulatory system.
16. The method of claim 11, wherein controlling the speed of the
pump comprises applying a different speed during the diastolic
phase than during the systolic phase for specified intervals that
are spaced by periods of rest.
17. The method of claim 17, wherein the specified intervals
comprise periods of one or more of decreasing speed during the
diastolic phase and increasing speed in the systolic phase to
incrementally reduce assistance provided to the circulatory system
by the pump.
18. The method of claim 11: wherein receiving data relating to a
physiological parameter comprises measuring a current applied to
the pump; wherein said current is correlated to an output of the
pump and the diastolic and systolic phases of the cardiac cycle;
and wherein said method further comprises identifying the diastolic
and systolic phases of the cardiac cycle as a function of the
measured current over time.
19. The method of claim 11: wherein receiving data relating to a
physiological parameter comprises measuring a physiological
parameter with a sensor; wherein said physiological parameter is
correlated to an output of the pump and the diastolic and systolic
phases of the cardiac cycle; and wherein said method further
comprises identifying the diastolic and systolic phases of the
cardiac cycle as a function of the measured physiological
parameter.
20. The method of claim 19, wherein the physiological parameter
comprises one or more of electrocardiogram measurements,
ventricular pressure measurements or ventricular volume
measurements.
21. A system for providing mechanical circulatory assistance to a
patient, the system comprising: (a) a left ventricular assist
device (LVAD) pump configured to be inserted into the patient's
circulatory system; (b) a processor; and (c) a non-transitory
memory storing instructions executable by the processor; (d)
wherein said instructions, when executed by the processor, perform
steps comprising: (i) receiving data relating to a physiological
parameter of the circulatory system; (ii) identifying diastolic and
systolic phases of the cardiac cycle of the circulatory system; and
(iii) controlling the speed of the pump to have a different speed
during the diastolic phase than during the systolic phase.
22. The system of claim 21, wherein controlling the speed of the
pump comprises increasing the speed of the pump during the
diastolic phase as compared to the systolic phase.
23. The system apparatus of claim 22: wherein said increased speed
during the diastolic phase results in an increased pumped diastolic
volume; and wherein said increased pumped diastolic volume
contributes to a smaller end diastolic volume and a diminished
starling response associated with a left ventricle of the
circulatory system.
24. The system of claim 21, wherein controlling the speed of the
pump comprises decreasing the speed of the pump during the systolic
phase as compared to the diastolic phase.
25. The system of claim 24: wherein said decreased speed of the
pump during the systolic phase results in an decreased pumped
diastolic volume; and wherein said decrease pumped systolic volume
contributes to a decrease in pressure in an aorta associated with
the circulatory system.
26. The system of claim 21, wherein controlling the speed of the
pump comprises applying a different speed during the diastolic
phase than during the systolic phase for specified intervals that
are spaced by periods of rest.
27. The system of claim 26, wherein the specified intervals
comprise periods of one or more of decreasing speed during the
diastolic phase and increasing speed in the systolic phase to
incrementally reduce assistance provided to the circulatory system
by the pump.
28. The system of claim 21: wherein receiving data relating to a
physiological parameter comprises measuring a current applied to
the pump; wherein said current is correlated to an output of the
pump and the diastolic and systolic phases of the cardiac cycle;
wherein said instructions when executed by the processor further
perform steps comprising identifying the diastolic and systolic
phases of the cardiac cycle as a function of the measured current
over time.
29. The system of claim 21, further comprising: one or more sensors
coupled to the processor; wherein receiving data relating to a
physiological parameter comprises measuring a physiological
parameter with the one or more sensors; wherein said physiological
parameter is correlated to an output of the pump and the diastolic
and systolic phases of the cardiac cycle; and wherein said
instructions when executed by the processor further perform steps
comprising identifying the diastolic and systolic phases of the
cardiac cycle as a function of the measured physiological
parameter.
30. The system of claim 29, wherein the physiological parameter
comprises one or more of electrocardiogram measurements,
ventricular pressure measurements or ventricular volume
measurements.
31. The system of claim 21, further comprising: an external device
coupled on the pump; wherein the external device comprises said
instructions to remotely control the speed of the pump from a
location external to the patient.
32. The system of claim 31: wherein said instructions are
configured to allow user input of a target physiological metric;
and wherein controlling the speed of the pump comprises: (i)
calculating a change in pump speed for one or more of the diastolic
phase and the systolic phase based on the target physiological
metric; and (ii) sending a command to the pump to change the pump
speed at a specified period timed according to one or more of the
diastolic phase and the systolic phase.
33. The system of claim 32, wherein said instructions are further
configured to perform the steps of: (iv) receiving data relating to
an adjusted physiological parameter of the circulatory system
resulting from the change in pump speed; (v) comparing the target
physiological metric to the adjusted physiological parameter; and
(vi) calculating an adjusted change in pump speed in response to
the target physiological metric not being met.
34. The system of claim 31, wherein the target physiological metric
comprises a ratio of diastolic volume to systolic volume.
35. The system of claim 31, wherein the external device comprises a
user interface configured to allow user input of the target
physiological metric.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION
[0003] A portion of the material in this patent document may be
subject to copyright protection under the copyright laws of the
United States and of other countries. The owner of the copyright
rights has no objection to the facsimile reproduction by anyone of
the patent document or the patent disclosure, as it appears in the
United States Patent and Trademark Office publicly available file
or records, but otherwise reserves all copyright rights whatsoever.
The copyright owner does not hereby waive any of its rights to have
this patent document maintained in secrecy, including without
limitation its rights pursuant to 37 C.F.R. .sctn. 1.14.
BACKGROUND
1. Technical Field
[0004] The technology of this disclosure pertains generally to
cardiac devices, and more particularly to mechanical circulatory
support devices.
2. Background Discussion
[0005] Congestive heart failure (CHF) is a major, rapidly growing
public health problem, with a prevalence of more than 5.8 million
in the United States and more than 23 million worldwide that
results in hundreds of thousands of deaths annually. After the
diagnosis of CHF, survival estimates are 50% and 10% at 5 and 10
years, respectively, and left ventricular dysfunction is associated
with an increase in the risk of sudden death. Patients with end
stage heart failure who are refractory to medications, surgical
intervention and resynchronizer pacing are best treated with
cardiac transplantation. However, donor hearts are limited to about
2,000 per year in the United States and, consequently, there is a
large unmet need for approximately 75,000 patients who would
benefit from cardiac transplantation, but for whom no donor heart
is available.
[0006] Extensive research since the mid 1960's has resulted in
numerous surgically implanted left ventricular assist devices
(LVAD) intended to take over part or all of the work of the left
ventricle while working in parallel with the native heart. First
generation LVAD's were based on biomimicry and emulated the pulse
using positive displacement pumps. Although these technologies
demonstrated potential clinical benefit, they had limited
durability. The current generation of LVAD's is based on rotary
pump technologies and has proven to be effective, durable, and
result in significant reduction in pulsatility. Rotary pumps impart
kinetic energy to a fluid, as velocity, by means of rotating blades
to provide continuous flow. The velocity energy of the fluid is
then converted to static pressure to move blood through the
circulation. A major advantage of rotary LVADs is superior
durability, sometimes running for over 10 years.
[0007] The three commercially available rotary LVAD's in clinical
use in the United States are, the HeartMate II and HeartMate III
owned by Abbott, Inc. and the HeartWare HVAD owned by Medtronic,
Inc. These devices have demonstrated the ability to support
systemic circulation and have been effective in bridging patients
to cardiac transplantation. In addition, these devices have
demonstrated the ability to support patients who are not candidates
for transplantation for as long as 10 years, so called
`destination` patients. However, expectations that patients would
recover during LVAD support and, ultimately, be weaned from support
have not been realized.
[0008] The poor weaning results (<5%) are not understood.
Failure to achieve sufficient myocardial recovery to permit weaning
may be due to the fact that the myocardium is irreversibly damaged.
Alternately, it may be that the limitations of existing pump
control do not lend itself to optimally conditioning the
myocardium.
[0009] Although existing LVAD's provide greatly improved
circulatory support for patients in heart failure, and provide
successful bridging to transplantation and long term support, they
are very limited in their ability to meet the dynamic demands of
the heart and circulation. Presently, they operate only under speed
control, meaning the motor strives to maintain speed regardless of
the load using a closed loop algorithm. If there is a clinical
reason to vary speed, the only control available to the clinician
is to manually adjust the speed of the pump during clinic visits.
The speed cannot be changed remotely by the physician, nor can the
patient adjust the speed. In fact, there is no intelligence in
existing LVADs to automatically adjust to changing clinical
conditions of patients. For this reason the pumps are `dumb` in
that the degree of assistance is determined only by the pressure
gradient against which it is pumping. Consequently, most of the
flow occurs during systole, when the pressure difference between
the inlet and outlet is low, and significantly less during
diastole, when the pressure difference is greater. This behavior of
the LVAD is driven by the pressure difference imposed by the
ventricle across the pump inlet to outlet whether or not the
ventricle might benefit from a different strategy.
[0010] Given the limitations of existing rotary LVADs, only the
speed can be adjusted to encourage myocardial recovery. The present
weaning strategy, typically, lowers the pump speed based on a `ramp
test` with the intention of increasing the work load of the heart
for a period of months. Ramp testing provides an assessment of
ventricular performance by measuring the dilation of the heart in
response to trials of decreased pump speed. Some patients tolerate
decreased assistance and may well become weanable, but they also
may be in a state of increased heart failure compared to their
clinical state at a previous higher speed.
[0011] Accordingly, an objective of the present disclosure is a
system and method for LVAD treatment to affect myocardial recovery
and thus make it possible to remove the device or increase the
number of patients weaned from support. With an increase in weaning
rates the need for cardiac transplantation may be decreased, and
mechanical circulatory assistance may be employed as a definitive
treatment, rather than bridging to transplantation or palliative
care. In addition, LVADs could be used on less sick patients as a
therapy to recovery and weaning rather than transplantation.
BRIEF SUMMARY
[0012] An aspect of the present disclosure is a system and method
for changing one or more characteristics (e.g. flow magnitude via
pump speed) of mechanical circulatory assistance provided by a left
ventricular assist device (LVAD) during the cardiac cycle using
closed loop control.
[0013] Another aspect is a system and method for dynamically
changing ventricular unloading during the cardiac cycle in patients
who are recipients of left ventricular assist devices LVADs. The
system and methods provide for a platform to adjust the degree of
ventricular assistance, independently, during systole and/or
diastole. The system and methods also provide for a means to sense
the phase of the cardiac cycle to inform the LVAD of timing within
the cardiac cycle.
[0014] One method for dynamic ventricular unloading (DVU) in
accordance with the present description is the optimization of
mechanical ventricular assistance to affect a higher rate of heart
recovery and increase the ability of clinicians to wean patients
from LVAD support.
[0015] Another method for dynamic ventricular unloading in
accordance with the present description is the reduction of the
residence time of the blood in the ventricle to minimize thrombosis
and strokes.
[0016] Further aspects of the technology described herein will be
brought out in the following portions of the specification, wherein
the detailed description is for the purpose of fully disclosing
preferred embodiments of the technology without placing limitations
thereon.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0017] The technology described herein will be more fully
understood by reference to the following drawings which are for
illustrative purposes only:
[0018] FIG. 1 shows a high-level schematic diagram of a system for
providing mechanical circulatory assistance provided by a left
ventricular assist device (LVAD) during the cardiac cycle.
[0019] FIG. 2A and FIG. 2B show graphs of flow pulsatility, before
(FIG. 2A) and after (FIG. 2B) manipulation via Dynamic Ventricular
Unloading (DVU) in accordance with the present description.
[0020] FIG. 3 shows a schematic flow diagram for a method for
providing dynamic ventricular unloading via an LVAD pump in
accordance with the present description.
[0021] FIG. 4 illustrates a graph showing the hydraulic performance
(flow vs. head pressure) for a typical LVAD pump at varying
speeds.
[0022] FIG. 5 shows an exemplary user interface for operating an
LVAD pump with dynamic ventricular unloading.
DETAILED DESCRIPTION
[0023] The present description is directed to controlling the
distribution of assistance during the cardiac cycle for improved
heart muscle function, and in particular optimize the degree of
ventricular unloading generated by a left ventricular assist device
(LVAD) device during the acute phase of treatment. Once the
condition has stabilized, precise control of reloading of the heart
may be applied to increase the strength of ventricular contraction,
optimally leading to the removal of the LVAD device from the
patient. Removal of the device would permit the patient to return
to a more normal life style. Weaning is also desirable because risk
of significant adverse events, including severe stroke, increases
with time, thus the incidence of adverse events would be expected
to decrease.
[0024] In one embodiment, the cardiac muscle is conditioned by
timing operation of the LVAD to `work out` the heart with short
intervals of increased exertion followed by periods of rest,
similar to strategies used to condition skeletal muscle. Such an
exercise program, administered over a period of (e.g. months),
would `work out` the heart according to a scheduled regimen of
gradually increasing exertion with rest. The systems and method of
the present invention would ideally provide an LVAD with the
ability to adjust the level of assistance during the cardiac cycle
to precisely control the work load of the heart from beat to beat
(e.g. intra-beat manipulation) and would have the ability to
gradually and precisely decrease or increase ventricular support as
desired. As recovery progresses, the exercise regimen may be
adjusted to greater exertion to maximize conditioning and permit
removal of the LVAD.
[0025] FIG. 1 shows a high-level schematic diagram of a system 10
for providing mechanical circulatory assistance provided by an LVAD
pump 20 during the cardiac cycle. The LVAD pump 20 is disposed
within the circulatory system so as to receive blood at input 36
and provide circulatory assistance via blood output 38. LVAD pump
20 generally comprises a motor 22, power supply 24 (e.g. battery of
like power source) supplying voltage to the motor 22, and
programming and circuitry to control operation of the motor 22,
such as application software 28 stored in memory 30 for execution
on processor 26. Application software 28 generally comprises
instructions executable on processor 26, which together operate as
controller 25 commutate the motor 22 and directly supply driving
power to the motor 22, in addition to determining, maintaining, and
changing the motor speed via speed control commands 44. Where
direct wiring is not used, pump 20 may also comprise wireless
circuitry 32 (e.g. Wi-Fi, Bluetooth, or like wireless communication
protocol) for communicating with one or more sensors 34 and one or
more external devices 50. In an alternative embodiment, the sensor
34 and/or external device 50 may be hard-wired to the pump 20.
[0026] Alternatively, or in addition to data 42 acquired from
sensor 34, current measurement data 40 may also be acquired
relating to the current provided to the motor 22 (e.g. via power
supply 24), and used as a source of feedback to determine flow rate
and timing of the heart cycle, as will be explained in further
detail below. In typical rotary pumps, very low impedance
resistors/transistors 45 are in series with power and commands 44
being delivered to the motor 22 from the controller 25. The voltage
drop across the reference resistors 45 may be measured, and then
current may be calculated on basis of equation IR=V. Current data
40, and/or sensor data 42 may be used to determine the timing of
the cardiac cycle, or other physiological characteristics, to
adjust the speed (via a speed control command 44) of the motor
during differing stages of the cardiac cycle.
[0027] In one embodiment, external device 50 may comprise a cell
phone, computer, wearable controller, or other processing device
that has application software 56 for communicating with and/or
controlling the pump 20. The external device 50 preferably
comprises a processor 54 for executing application software 56 that
is stored in memory 58, and optional wireless circuitry 52 for
communicating with the pump 20 if direct wiring is not used. An
external sensor 60 may also be provided for acquiring physiological
data 62 from the patient, the data 62 being in addition to, or
replacement of data 42 from sensor 34. External device application
software 56 may also include a user interface 64 for displaying
data and/or control functionality with respect to sensors 60/34 and
pump 20.
[0028] As will be explained in further detail below, one or more of
the pump application software 28 and external device application
software 56 may include instructions for controlling the pump 20
via a method 100 for dynamic ventricular unloading (DVU) via
continuous feedback provided by input from one or more of motor
current data 40 and sensor data 42/62, as shown in FIG. 3 and
provided in further detail below.
[0029] FIG. 2A and FIG. 2B show graphs of the instantaneous pump
output flow over time, i.e. pulsatility curve 80, before (FIG. 2A)
and after (FIG. 2B) manipulation via Dynamic Ventricular Unloading
(DVU) in accordance with the present description. The pulsatility
curve 80 in the cardiac cycle will have a systolic phase (and
corresponding systolic volume V.sub.s) that includes an increasing
flow through the peak flow 82 that then generally decreases to the
waveform trough 84, and a diastolic phase (and corresponding
diastolic volume V.sub.D) that starts at the trough 84 and extends
until the systolic phase. Dynamic ventricular unloading (DVU), in
accordance with the methods disclosed herein, is performed by
actively changing the degree of unloading during the cardiac cycle
rather than unloading based exclusively on the pressure gradient
across the LVAD pump 20, thus allowing for the adjustment the ratio
of volume occurring during diastole/systole simply by changing the
pump speed 44 during the cardiac cycle.
[0030] For example, increasing pump speed 44 and corresponding
blood output flow 38 (FIG. 1) during diastole increases diastolic
volume output by the pump 20 to create an adjusted pumped diastolic
volume V.sub.DA, as shown in FIG. 2B. It should be noted that
diastolic volume V.sub.DA is the volume generated by the pump, and
is not to be confused with end diastolic volume (EDV), which is
generally understood to mean the volume of blood in the right
and/or left ventricle at the end load or filling in diastole. This
adjusted diastolic volume V.sub.DA has the anatomical affect of a
smaller end diastolic volume and a diminished starling response of
the ventricle. In addition, the smaller end diastolic volume
results in a smaller ventricular wall radius and reduces the wall
tension needed to maintain a given pressure. The above condition
would maximally unload the ventricle by reducing myocardial oxygen
requirements and produce a significant diastolic augmentation that
will increase perfusion of the recovering myocardium.
[0031] In addition (or alternatively) to the above, output 38
during systole could be decreased by decreasing pump speed 44 to
decrease the systolic volume (see adjusted systolic volume V.sub.SA
in FIG. 2B). This would affect a decrease in pressure in the aorta
and decrease in after load on the ventricle to facilitate recovery
during the initial phase following LVAD implantation.
[0032] After the acute phase of recovery, it may be desirable to
evaluate the status of the ventricle and attempt to wean from the
patient from LVAD support by decreasing the ratio of assistance
during diastole over systole, thus requiring the heart to perform
more work. To increase ventricular work, the pump speed 44 and flow
38 would be decreased during diastole, which would result in an
increase in the end diastolic volume. Such a maneuver would
increase the starling response and increase the wall radius, thus
requiring more wall tension and more myocardial work. Flow 38
during systole could also be increased to increase pressure in the
aorta and increase after load on the ventricle. The above would
also allow for a physician to run a ramp test while observing the
behavior of the heart as the ratio of diastolic and systolic flow
was varied, rather than just changing the average pump speed. While
the above scenarios may actually be better described as Dynamic
Ventricular Reloading (DVR), it is appreciated that DVU may be used
interchangeably for all Dynamic Ventricular Assistance (DVA)
scenarios.
[0033] FIG. 3 shows a schematic flow diagram for a method 100 for
providing dynamic ventricular unloading via an LVAD pump 20 in
accordance with the present description. Method 100 may be carried
out as instructions included in one more of application software 28
of pump 20 and application software 56 of external device 50.
[0034] Method 100 assumes an LVAD pump configured to gain access to
the circulatory system of the patient such that blood can be
removed from the left ventricle and pressurized into the aorta. In
one exemplary method, a pump 20 is surgically implanted such that
an inflow cannula (not shown) is inserted into the ventricular
cavity to provide input 36 to the pump. The pump output 38 connects
to the aorta via an artificial artery. Blood is then removed from
the left ventricle via the inflow cannula and pumped into the
aorta, thus, directly assisting the left ventricle. It is
appreciated that the above pump implementation is provided for
exemplary purposed only, and is not intended to be exhaustive of
presently available techniques for circulatory assistance. It is
appreciated that the systems and methods disclosed herein may be
integrated with, or provided as an add on, for any number of
circulatory assistance pumps available in the art.
[0035] As provided above, dynamic ventricular unloading adjusts the
balance of blood flow between diastole and systole by changing the
pump speed 44 of the LVAD pump 20 during the cardiac cycle. To
accommodate this, synchronization of the pump 20 with the cardiac
cycle is performed via closed loop control by acquiring a signal at
step 110 that identifies the phase(s) of contraction, e.g. flow
data such as the flow pulsatility curve 80, to identify systole and
diastole events/phases in the cardiac cycle. A number of signals
may be used, including a signal of the motor current data 40, or
sensor data 42/62 from one or more internal or external sensors in
the form of an ECG leads (electrocardiogram measurements),
intraventricular pressure or volume transducers (left side pressure
or ventricular volume measurements).
[0036] The patient's EKG would provide a reliable and stable
signal, but would typically involve implanted leads in the
myocardium and additional signal processing. A preferred embodiment
would use the motor current 44 as a surrogate to sense timing of
the pulse rate, systole and diastole. As explained in further
detail below, method 100 may be configured to detect onset of
systole and diastole to trigger speed changes. In addition, the
current signature from data 44 may be used as a surrogate to
measure LVAD flow and could be used to calculate the ratio of flow
during diastole and systole, and then seek the desired ratio of
flow during diastole versus systole. A ventricular pressure volume
loop may also be implemented to further evaluate the effect of the
dynamic assistance.
[0037] With respect to motor current data 40, generally there is a
direct correlation between the current applied to the motor and the
blood flow rate. This pump-specific data may be used to determine
flow rate, and the corresponding phase of the cardiac cycle, by
identifying the change in motor current over time.
[0038] This data acquisition is performed in real time, to
accommodate for changes in heart rate, and allow for rapid change
in speeds during the cardiac cycle, as well provide
instructions/control the pump 20 to change speed by a predetermined
protocol.
[0039] With the acquired data from step 110, the flow pulsatility
curve may be generated, and systole and diastole phases identified
to calculate systolic volume V.sub.s and diastolic volume V.sub.D
(FIG. 2A) at step 112 by integrating under the curve at respective
identified timeframes. The ratio of flow during diastole and
systole may then be calculated, e.g. as either V.sub.D/V.sub.s or
V.sub.D/(V.sub.D+V.sub.s), or any desired arithmetic or algebraic
formula.
[0040] At step 114, a desired systolic/diastolic volume adjustment
is calculated based on the pump flow or flow ratio in relation to a
target flow or flow ratio. The target flow is preferably based on a
treatment protocol that is desired for the patient at that time
(e.g. ventricular unloading for acute recovery phase, and
ventricular reloading for weaning the patient off the pump).
[0041] At step 116, the algorithm then calculates a motor speed
adjustment that is predicted to affect the desired
systolic/diastolic volume adjustment and corresponding target flow,
and sends a command to the motor 22 to change speed accordingly
(e.g. increasing motor speed in diastole and/or decreasing or
shutting off the motor in systole). The motor speed adjustment may
be calculated as a function of a number of factors, including the
patient's stroke volume, the blood input flow 36, blood output flow
38, pump speed, pulse rate, etc. The motor speed adjustment is
timed with respect to the cardiac cycle based on the pulsatility
curve, or other physiological sensor data acquired at step 110. It
is appreciated that because of transmission delay, and lag in pump
speed manipulation, that timing of the speed adjustment instruction
44 (FIG. 1) may well precede the actual event (e.g. a command to
increase speed during diastole may be initiated at some point in
systole).
[0042] In order to execute DVU, the LVAD pump 20 is preferably
configured to be able to change speeds (i.e. slew rate) rapidly
within the cardiac cycle. The slew rate of a pump is generally
defined as change in rpm/second, and is typically determined by the
design of the motor. In a preferred embodiment, a pump having a
slew rate of at least 1500 rpm would be desirable.
[0043] Furthermore, rotary LVAD pumps typically have a `slip,`
which means that for a given speed, the flow produced at higher
pressure is significantly less than at lower pressures. The
hydraulic performance of the HeartWare HVAD.TM. is shown in FIG. 4.
As an example, based on the hydraulic performance in the graph of
FIG. 4, the flow at 2,400 rpm is 2 lpm @ 100 mm Hg. Increasing the
speed to 3,000 rpm would increase the flow to 6 lpm @ 100 mm Hg.
The total time to change speed would be 600 rpm/2000 rpm/second or
300 milliseconds. This implies the ability to dynamically support a
heart rate of about 100 bpm. Optimization of the pump 20 may also
be implemented increase the slew rate if needed. In a preferred
embodiment, the LVAD pump 20 is able to deliver maximum flow rate
of at least 5 liters per minute at a pressure of 90 mm Hg.
[0044] At step 118, flow data is reacquired via additional input
from one or more of current data 40 and sensor data 42/62. The
sensitivity of this feedback (e.g. how many heartbeats or seconds
between the adjustment and step 116 and reacquisition at step 118)
may be adjusted as desired by the physician.
[0045] At step 120, the acquired data from step 118 is used to
calculate adjusted systolic volume V.sub.SA and adjusted diastolic
volume V.sub.DA (e.g. by regenerating the flow pulsatility curve,
and identifying systole and diastole phases as shown in FIG.
2B).
[0046] In addition, rotary pumps are capable of creating
significant negative pressure at the pump inlet 36, which can
result in `sucking down` on the endocardial surface of the heart,
effectively blocking the pump inlet 36. As pump speed is increased
during diastole with a resultant decrease in VEDV, the risk of
`suck down` may be increased. Consequently, `suck down` detection
will be necessary to mitigate this undesirable behavior.
[0047] At step 122, V.sub.SA and V.sub.DA or a ratio thereof (e.g.
either V.sub.DA/V.sub.SA or V.sub.DA/(V.sub.DA+V.sub.SA, or other
metric) are compared against the target volume metric. If target
ratio or other metric is not achieved, another systolic/diastolic
volume adjustment is calculated at step 124 to affect another
change in motor speed at step 116. Steps 118 through 122 are then
repeated in the feedback loop shown in FIG. 3.
[0048] It is appreciated that while systolic/diastolic volume
ratios are provided as the target metric in the above stems, any
number of physiological characteristics (e.g. stroke work index,
ejection fraction, etc.) may be used as the target metric, as
preferred by the physician.
[0049] The query at step 122 may also poll the obtained flow data
at 118 for the timing of the adjusted pulsatility curve 80b
(contrasted with original curve 80a in FIG. 2B) and readjust the
timing of the speed control command 44 if there are any variations
necessitating it (e.g. change or offset in heart rate).
[0050] If query step 122 reveals that the target ratio or other
metric is achieved, than the algorithm continues to poll the
sensors to obtain flow data at step 118 at the specified
sensitivity increment, and steps 120 through 122 are then repeated
in the feedback loop shown in FIG. 3.
[0051] As the systolic/diastolic volume ratio is adjusted,
conventional clinical metrics can be employed to assess the
patient's status. This could include non-invasive modalities such
as the EKG, blood pressure, pulse oximetry etc. Invasive tests
could include placement of a Swan Gantz catheter for measurement of
mixed venous saturation, right sided pressures and cardiac output.
During the weeks to months after DVU adjustment the response of the
myocardium can be assessed by echocardiography and various blood
markers that measure myocardial injury (enzymes) and heart failure
(BPN, troponin).
[0052] FIG. 5 illustrates an exemplary user interface 64 that may
be implemented as application software 56 (FIG. 1). User interface
64 comprises a physician or patient screen 150 that shows pump
status in a number of a number of indicators (e.g. average pump
flow 170, average pump speed 172, average power 174, and operating
mode 176 (e.g. a variable speed mode where the speed of the motor
22 is a varied according to an intra-beat control scheme as
detailed in FIG. 3, fixed or constant speed mode, etc.)). A number
of graphical buttons 180 may be provided for various modules that
are available to the physician and/or patient. A live plot 152 may
be output, e.g. showing pump or physiology characteristics such as
the flow pulsatility 80.
[0053] Each module may have a plurality of tabs 184-188. For
example, flow tab 184 may include a field 192 for inputting flow
characteristics e.g. target V.sub.D/V.sub.s compared to the
measured or present ratio 190. Power tab 186 may be toggled to
adjust the work performed by the pump during the cardiac cycle (in
units of watts). Time tab 188 may be toggled to set the ratio of
time spent pumping during diastole and systole.
[0054] Additional tabs may be provided for time settings 156, alarm
settings 158 for events such as high or low current, low flow, suck
down, setup 160 and speed control 162. For example, time settings
tab 156 may be employed for setting timing for particular
intermittent workouts (e.g. for weaning protocols) or duration of
assistance or timing of assistance for different phases of recovery
(e.g. maximum ventricular unloading for the acute recover phase).
Setup tab 160 may provide the physician with desired
sensor/feedback input (e.g. pressure, ECG, current sensing, etc.),
sensitivity.
[0055] Display 152 may also provide a flow pulsatility modification
screen similar to that shown in FIG. 2B. In such configuration, the
pulsatility curve 80 that has selectable points in which the
physician may simply drag on the screen to shape the curve 80 to a
desired profile. For example, the physician could drag the systole
peak from 90a to 90b (showing a desired target peak from line 82 to
86), or drag a diastole point from 92a to 92b (e.g. from just above
trough 84 to line 88. The algorithm 100 would then use that profile
as the target profile at which the speed command 44 and timing is
set.
[0056] The user interface 64 may also include indicators showing
various status characteristics of the pump 20. For example, a
battery indicator 164 may provide the status of the battery 24
(e.g. percentage of life) and wireless connectivity status
indicator 178 may show wireless connection strength with the pump
20.
[0057] The systems and methods described above for DVU would
provide optimized performance of LVAD's to improve the clinical
course of LVAD patients and to improve their quality of life. The
following benefits to patients are anticipated: 1) increased rate
of weaning from LVAD support and decreased exposure time to the
risk of adverse events secondary to the device, 2) improved washing
around the apex tube due to smaller EDV and higher flow rates
during diastole would decrease the incidence of thrombus formation,
3) greater control over the opening of the aortic valve to maximize
washing of the leaflets, 4) increased diastolic augmentation of
blood to the heart, and 5) greater durability of weaning.
[0058] As an alternative to the above systems and methods, a pump
may be configured or programmed to operate under passive, open-loop
control. Typically, rotary LVADs use active speed control with a
closed-loop control. However, it is possible to run open loop or
with simple voltage control. With an open-loop pump under this
embodiment, the speed will vary depending upon the load, i.e. the
larger the load (e.g. flow) will slow the pump down and the lesser
load, the pump will speed up. With respect to rotary pump behavior,
if the outlet is clamped (e.g. delta pressure increased) the power
drops, so the pump speeds up and pumps more flow up to the current
limit. This would be indicative of operation of the pump during
diastole. If there is very small delta pressure (as in systole),
the pump will not be able to maintain speed because of increased
volume presented to the pump, and the current limit will slow down
pump, resulting in lower flow. The net effect is that with an
open-loop control scenario as described in this embodiment, the
ratio of the volume pumped during diastole will be greater than
with closed loop speed control, thus passively creating a more
favorable pumping scheme than with a pump having closed-loop
control and constant speed.
[0059] Embodiments of the present technology may be described
herein with reference to flowchart illustrations of methods and
systems according to embodiments of the technology, and/or
procedures, algorithms, steps, operations, formulae, or other
computational depictions, which may also be implemented as computer
program products. In this regard, each block or step of a
flowchart, and combinations of blocks (and/or steps) in a
flowchart, as well as any procedure, algorithm, step, operation,
formula, or computational depiction can be implemented by various
means, such as hardware, firmware, and/or software including one or
more computer program instructions embodied in computer-readable
program code. As will be appreciated, any such computer program
instructions may be executed by one or more computer processors,
including without limitation a general purpose computer or special
purpose computer, or other programmable processing apparatus to
produce a machine, such that the computer program instructions
which execute on the computer processor(s) or other programmable
processing apparatus create means for implementing the function(s)
specified.
[0060] Accordingly, blocks of the flowcharts, and procedures,
algorithms, steps, operations, formulae, or computational
depictions described herein support combinations of means for
performing the specified function(s), combinations of steps for
performing the specified function(s), and computer program
instructions, such as embodied in computer-readable program code
logic means, for performing the specified function(s). It will also
be understood that each block of the flowchart illustrations, as
well as any procedures, algorithms, steps, operations, formulae, or
computational depictions and combinations thereof described herein,
can be implemented by special purpose hardware-based computer
systems which perform the specified function(s) or step(s), or
combinations of special purpose hardware and computer-readable
program code.
[0061] Furthermore, these computer program instructions, such as
embodied in computer-readable program code, may also be stored in
one or more computer-readable memory or memory devices that can
direct a computer processor or other programmable processing
apparatus to function in a particular manner, such that the
instructions stored in the computer-readable memory or memory
devices produce an article of manufacture including instruction
means which implement the function specified in the block(s) of the
flowchart(s). The computer program instructions may also be
executed by a computer processor or other programmable processing
apparatus to cause a series of operational steps to be performed on
the computer processor or other programmable processing apparatus
to produce a computer-implemented process such that the
instructions which execute on the computer processor or other
programmable processing apparatus provide steps for implementing
the functions specified in the block(s) of the flowchart(s),
procedure (s) algorithm(s), step(s), operation(s), formula(e), or
computational depiction(s).
[0062] It will further be appreciated that the terms "programming"
or "program executable" as used herein refer to one or more
instructions that can be executed by one or more computer
processors to perform one or more functions as described herein.
The instructions can be embodied in software, in firmware, or in a
combination of software and firmware. The instructions can be
stored local to the device in non-transitory media, or can be
stored remotely such as on a server, or all or a portion of the
instructions can be stored locally and remotely. Instructions
stored remotely can be downloaded (pushed) to the device by user
initiation, or automatically based on one or more factors.
[0063] It will further be appreciated that as used herein, that the
terms processor, hardware processor, computer processor, central
processing unit (CPU), and computer are used synonymously to denote
a device capable of executing the instructions and communicating
with input/output interfaces and/or peripheral devices, and that
the terms processor, hardware processor, computer processor, CPU,
and computer are intended to encompass single or multiple devices,
single core and multicore devices, and variations thereof.
[0064] From the description herein, it will be appreciated that the
present disclosure encompasses multiple embodiments which include,
but are not limited to, the following:
[0065] 1. An apparatus for providing mechanical circulatory
assistance provided by an implanted left ventricular assist device
(LVAD) pump, the apparatus comprising: (a) a processor; and (b) a
non-transitory memory storing instructions executable by the
processor; (c) wherein said instructions, when executed by the
processor, perform steps comprising: (i) receiving data relating to
a physiological parameter of a circulatory system in which the
implanted LVAD pump is operating; (ii) identifying diastolic and
systolic phases of the cardiac cycle of the circulatory system; and
(iii) controlling the speed of the pump to have a different speed
during the diastolic phase than during the systolic phase.
[0066] 2. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises increasing the speed of the pump during the diastolic
phase as compared to the systolic phase.
[0067] 3. The apparatus, method, or system of any preceding or
following embodiment: wherein said increased speed during the
diastolic phase results in an increased pumped diastolic volume;
and wherein said increased pumped diastolic volume contributes to a
smaller end diastolic volume and a diminished starling response
associated with a left ventricle of the circulatory system.
[0068] 4. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises decreasing the speed of the pump during the systolic
phase as compared to the diastolic phase.
[0069] 5. The apparatus, method, or system of any preceding or
following embodiment: wherein said decreased speed of the pump
during the systolic phase results in an increased pumped diastolic
volume; and wherein said increased pumped systolic volume
contributes to a decrease in pressure in an aorta associated with
the circulatory system.
[0070] 6. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises applying a different speed during the diastolic phase
than during the systolic phase for specified intervals that are
spaced by periods of rest.
[0071] 7. The apparatus, method, or system of any preceding or
following embodiment, wherein the specified intervals comprise
periods of one or more of decreasing speed during the diastolic
phase and increasing speed in the systolic phase to incrementally
reduce assistance provided to the circulatory system by the
pump.
[0072] 8. The apparatus, method, or system of any preceding or
following embodiment: wherein receiving data relating to a
physiological parameter comprises measuring a current applied to
the pump; wherein said current is correlated to an output of the
pump and the diastolic and systolic phases of the cardiac cycle;
and wherein said instructions when executed by the processor
further perform steps comprising identifying the diastolic and
systolic phases of the cardiac cycle as a function of the measured
current over time.
[0073] 9. The apparatus, method, or system of any preceding or
following embodiment: wherein receiving data relating to a
physiological parameter comprises measuring a physiological
parameter with a sensor; wherein said physiological parameter is
correlated to an output of the pump and the diastolic and systolic
phases of the cardiac cycle; and wherein said instructions when
executed by the processor further perform steps comprising
identifying the diastolic and systolic phases of the cardiac cycle
as a function of the measured physiological parameter.
[0074] 10. The apparatus, method, or system of any preceding or
following embodiment, wherein the physiological parameter comprises
one or more of electrocardiogram measurements, ventricular pressure
measurements or ventricular volume measurements.
[0075] 11. A method for providing mechanical circulatory assistance
provided by a left ventricular assist device (LVAD) pump, the
method comprising: installing an LVAD within a circulatory system
of a patient; receiving data relating to a physiological parameter
of the circulatory system; identifying diastolic and systolic
phases of the cardiac cycle of the circulatory system; and
controlling the speed of the pump to have a different speed during
the diastolic phase than during the systolic phase.
[0076] 12. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises increasing the speed of the pump during the diastolic
phase as compared to the systolic phase.
[0077] 13. The apparatus, method, or system of any preceding or
following embodiment: wherein said increased speed during the
diastolic phase results in an increased pumped diastolic volume;
and wherein said increased pumped diastolic volume contributes to a
smaller end diastolic volume and a diminished starling response
associated with a left ventricle of the circulatory system.
[0078] 14. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises decreasing the speed of the pump during the systolic
phase as compared to the diastolic phase.
[0079] 15. The apparatus, method, or system of any preceding or
following embodiment: wherein said decreased speed of the pump
during the systolic phase results in a decreased pumped diastolic
volume; and wherein said decreased pumped systolic volume
contributes to a decrease in pressure in an aorta associated with
the circulatory system.
[0080] 16. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises applying a different speed during the diastolic phase
than during the systolic phase for specified intervals that are
spaced by periods of rest.
[0081] 17. The apparatus, method, or system of any preceding or
following embodiment, wherein the specified intervals comprise
periods of one or more of decreasing speed during the diastolic
phase and increasing speed in the systolic phase to incrementally
reduce assistance provided to the circulatory system by the
pump.
[0082] 18. The apparatus, method, or system of any preceding or
following embodiment: wherein receiving data relating to a
physiological parameter comprises measuring a current applied to
the pump; wherein said current is correlated to an output of the
pump and the diastolic and systolic phases of the cardiac cycle;
and wherein the diastolic and systolic phases of the cardiac cycle
are identified as a function of the measured current over time.
[0083] 19. The apparatus, method, or system of any preceding or
following embodiment: wherein receiving data relating to a
physiological parameter comprises measuring a physiological
parameter with a sensor; wherein said physiological parameter is
correlated to an output of the pump and the diastolic and systolic
phases of the cardiac cycle; and wherein the diastolic and systolic
phases of the cardiac cycle are identified as a function of the
measured physiological parameter.
[0084] 20. The apparatus, method, or system of any preceding or
following embodiment, wherein the physiological parameter comprises
one or more of electrocardiogram measurements, ventricular pressure
measurements or ventricular volume measurements.
[0085] 21. A system for providing mechanical circulatory assistance
to a patient, the system comprising: (a) a left ventricular assist
device (LVAD) pump configured to be inserted into the patient's
circulatory system; (b) a processor; and (c) a non-transitory
memory storing instructions executable by the processor; (d)
wherein said instructions, when executed by the processor, perform
steps comprising: (i) receiving data relating to a physiological
parameter of the circulatory system; (ii) identifying diastolic and
systolic phases of the cardiac cycle of the circulatory system; and
(iii) controlling the speed of the pump to have a different speed
during the diastolic phase than during the systolic phase.
[0086] 22. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises increasing the speed of the pump during the diastolic
phase as compared to the systolic phase.
[0087] 23. The apparatus, method, or system of any preceding or
following embodiment: wherein said increased speed during the
diastolic phase results in an increased pumped diastolic volume;
and wherein said increased pumped diastolic volume contributes to a
smaller end diastolic volume and a diminished starling response
associated with a left ventricle of the circulatory system.
[0088] 24. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises decreasing the speed of the pump during the systolic
phase as compared to the diastolic phase.
[0089] 25. The apparatus, method, or system of any preceding or
following embodiment: wherein said decreased speed of the pump
during the systolic phase results in an decreased pumped diastolic
volume; and wherein said decrease pumped systolic volume
contributes to a decrease in pressure in an aorta associated with
the circulatory system.
[0090] 26. The apparatus, method, or system of any preceding or
following embodiment, wherein controlling the speed of the pump
comprises applying a different speed during the diastolic phase
than during the systolic phase for specified intervals that are
spaced by periods of rest.
[0091] 27. The apparatus, method, or system of any preceding or
following embodiment, wherein the specified intervals comprise
periods of one or more of decreasing speed during the diastolic
phase and increasing speed in the systolic phase to incrementally
reduce assistance provided to the circulatory system by the
pump.
[0092] 28. The apparatus, method, or system of any preceding or
following embodiment: wherein receiving data relating to a
physiological parameter comprises measuring a current applied to
the pump; wherein said current is correlated to an output of the
pump and the diastolic and systolic phases of the cardiac cycle;
wherein said instructions when executed by the processor further
perform steps comprising identifying the diastolic and systolic
phases of the cardiac cycle as a function of the measured current
over time.
[0093] 29. The apparatus, method, or system of any preceding or
following embodiment, further comprising: one or more sensors
coupled to the processor; wherein receiving data relating to a
physiological parameter comprises measuring a physiological
parameter with the one or more sensors; wherein said physiological
parameter is correlated to an output of the pump and the diastolic
and systolic phases of the cardiac cycle; and wherein said
instructions when executed by the processor further perform steps
comprising identifying the diastolic and systolic phases of the
cardiac cycle as a function of the measured physiological
parameter.
[0094] 30. The apparatus, method, or system of any preceding or
following embodiment, wherein the physiological parameter comprises
one or more of electrocardiogram measurements, ventricular pressure
measurements or ventricular volume measurements.
[0095] 31. The apparatus, method, or system of any preceding or
following embodiment, further comprising: an external device
coupled on the pump; wherein the external device comprises said
instructions to remotely control the speed of the pump from a
location external to the patient.
[0096] 32. The apparatus, method, or system of any preceding or
following embodiment: wherein said instructions are configured to
allow user input of a target physiological metric; and wherein
controlling the speed of the pump comprises: (i) calculating a
change in pump speed for one or more of the diastolic phase and the
systolic phase based on the target physiological metric; and (ii)
sending a command to the pump to change the pump speed at a
specified period timed according to one or more of the diastolic
phase and the systolic phase.
[0097] 33. The apparatus, method, or system of any preceding or
following embodiment, wherein said instructions are further
configured to perform the steps of: (iv) receiving data relating to
an adjusted physiological parameter of the circulatory system
resulting from the change in pump speed; (v) comparing the target
physiological metric to the adjusted physiological parameter; and
(vi) calculating an adjusted change in pump speed in response to
the target physiological metric not being met.
[0098] 34. The apparatus, method, or system of any preceding or
following embodiment, wherein the target physiological metric
comprises a ratio of diastolic volume to systolic volume.
[0099] 35. The apparatus, method, or system of any preceding or
following embodiment, wherein the external device comprises a user
interface configured to allow user input of the target
physiological metric.
[0100] As used herein, the singular terms "a," "an," and "the" may
include plural referents unless the context clearly dictates
otherwise. Reference to an object in the singular is not intended
to mean "one and only one" unless explicitly so stated, but rather
"one or more."
[0101] As used herein, the term "set" refers to a collection of one
or more objects. Thus, for example, a set of objects can include a
single object or multiple objects.
[0102] As used herein, the terms "substantially" and "about" are
used to describe and account for small variations. When used in
conjunction with an event or circumstance, the terms can refer to
instances in which the event or circumstance occurs precisely as
well as instances in which the event or circumstance occurs to a
close approximation. When used in conjunction with a numerical
value, the terms can refer to a range of variation of less than or
equal to .+-.10% of that numerical value, such as less than or
equal to .+-.5%, less than or equal to .+-.4%, less than or equal
to .+-.3%, less than or equal to .+-.2%, less than or equal to
.+-.1%, less than or equal to .+-.0.5%, less than or equal to
.+-.0.1%, or less than or equal to .+-.0.05%. For example,
"substantially" aligned can refer to a range of angular variation
of less than or equal to .+-.10.degree., such as less than or equal
to .+-.5.degree., less than or equal to .+-.4.degree., less than or
equal to .+-.3.degree., less than or equal to .+-.2.degree., less
than or equal to .+-.1.degree., less than or equal to
.+-.0.5.degree., less than or equal to .+-.0.1.degree., or less
than or equal to .+-.0.05.degree..
[0103] Additionally, amounts, ratios, and other numerical values
may sometimes be presented herein in a range format. It is to be
understood that such range format is used for convenience and
brevity and should be understood flexibly to include numerical
values explicitly specified as limits of a range, but also to
include all individual numerical values or sub-ranges encompassed
within that range as if each numerical value and sub-range is
explicitly specified. For example, a ratio in the range of about 1
to about 200 should be understood to include the explicitly recited
limits of about 1 and about 200, but also to include individual
ratios such as about 2, about 3, and about 4, and sub-ranges such
as about 10 to about 50, about 20 to about 100, and so forth.
[0104] Although the description herein contains many details, these
should not be construed as limiting the scope of the disclosure but
as merely providing illustrations of some of the presently
preferred embodiments. Therefore, it will be appreciated that the
scope of the disclosure fully encompasses other embodiments which
may become obvious to those skilled in the art.
[0105] All structural and functional equivalents to the elements of
the disclosed embodiments that are known to those of ordinary skill
in the art are expressly incorporated herein by reference and are
intended to be encompassed by the present claims. Furthermore, no
element, component, or method step in the present disclosure is
intended to be dedicated to the public regardless of whether the
element, component, or method step is explicitly recited in the
claims. No claim element herein is to be construed as a "means plus
function" element unless the element is expressly recited using the
phrase "means for". No claim element herein is to be construed as a
"step plus function" element unless the element is expressly
recited using the phrase "step for".
* * * * *